The present invention relates to the art of optical integrated circuits and more particularly to apparatus and methods for providing arrayed waveguides having a center wavelength that is independent of temperature.
Optical integrated circuits (OICs) come in many forms such as 1xc3x97N optical splitters, optical switches, wavelength division multiplexers (WDMs), demultiplexers, optical add/drop multiplexers (OADMs), and the like. Such OICs are employed in constructing optical networks in which light signals are transmitted between optical devices for carrying data and other information. For instance, traditional signal exchanges within telecommunications networks and data communications networks using transmission of electrical signals via electrically conductive lines are being replaced with optical fibers and circuits through which optical (e.g., light) signals are transmitted. Such optical signals may carry data or other information through modulation techniques, for transmission of such information through an optical network. Optical circuits allow branching, coupling, switching, separating, multiplexing and demultiplexing of optical signals without intermediate transformation between optical and electrical media.
Such optical circuits include planar lightwave circuits (PLCs) having optical waveguides on flat substrates, which can be used for routing optical signals from one of a number of input optical fibers to any one of a number of output optical fibers or optical circuitry. PLCs make it possible to achieve higher densities, greater production volume and more diverse functions than are available with fiber components through employment of manufacturing techniques typically associated with the semiconductor industry. For instance, PLCs contain optical paths known as waveguides formed on a silicon wafer substrate using lithographic processing, wherein the waveguides are made from transmissive media, which have a higher index of refraction than the chip substrate or the outlying cladding layers in order to guide light along the optical path. By using advanced photolithographic and other processes, PLCs are fashioned to integrate multiple components and functionalities into a single optical chip.
One important application of PLCs in particular and OICs generally involves wavelength-division multiplexing (WDM) including dense wavelength-division multiplexing (DWDM). DWDM allows optical signals of different wavelengths, each carrying separate information, to be transmitted via a single optical channel or fiber in an optical network. For example, early systems provided four different wavelengths separated by 400 GHz, wherein each wavelength transferred data at 2.5 Gbits per second. Current multiplexed optical systems employ as many as 160 wavelengths on each optical fiber.
In order to provide advanced multiplexing and demultiplexing (e.g., DWDM) and other functions in such networks, arrayed-waveguide gratings (AWGs) have been developed in the form of PLCs. Existing AWGs can provide multiplexing or demultiplexing of up to 80 channels or wavelengths spaced as close as 50 GHz. As illustrated in FIG. 1, a conventional demultiplexing AWG 2 includes a single input port 3, and multiple output ports 4. Multiple wavelength light is received at the input port 3 (e.g., from an optical fiber in a network, not shown) and provided to an input lens 5 via an input optical path or waveguide 6.
The input lens 5 spreads the multiple wavelength light into an array of waveguides 7, sometimes referred to a waveguide grating. Each of the waveguides 7 has a different optical path length from the input lens 5 to an output lens 8, resulting in a different phase tilt at the input to the output lens 8 depending on wavelength. This phase tilt, in turn, affects how the light recombines in the output lens 8 through constructive interference. The output lens 8 thus provides different wavelengths at the output ports 4 via individual output waveguides 9, whereby the AWG 2 can be employed in demultiplexing light signals entering the input port 6 into two or more demultiplexed signals at the output port 4. The AWG 2 can alternatively be used to multiplex light signals from the ports 4 into a multiplexed signal having two or more wavelength components at the port 3.
One of the problems with optical integrated circuits, such as the conventional AWG 2 of FIG. 1 is temperature sensitivity. Since the waveguide material usually has a temperature dependent refractive index, the channel wavelengths of multi/demultiplexer shift as the temperature varies. This shift is typically of the order of 0.01 nm/E C in silica-based devices and 0.1 nm/E C in InP based devices. This wavelength shift can result in a loss of signal and/or cross talk in communication system(s) employing the AWG 2. As communication system(s) are designed with increasingly smaller channel spacing, even a small temperature dependent wavelength shift can have a significant effect on system performance. Presently, AWG=s must have active stabilization of the device operating temperature in order to perform acceptably. This stabilization is typically achieved by the addition of resistive heaters, temperature sensors, active electronics, and in some cases also thermoelectric coolers. Even though an AWG is a passive filter, currently it requires significant electronics and a few watts of power to operate effectively.
Accordingly, there remains a need for better solutions to temperature sensitivity in optical integrated circuits such as AWGs, which avoid or mitigate the performance reductions associated with conventional optical integrated circuits and provide for mitigation of active temperature stabilization and its associated costs.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Rather, the sole purpose of this summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented hereinafter.
The present invention provides athermal optical integrated circuits and methods for athermalizing optical integrated circuits mitigating and/or overcoming the shortcomings associated with conventional optical integrated circuit(s) and other devices. The invention further comprises methods for fabricating OICs and for mitigating temperature sensitivity utilizing a groove and an actuator. Markedly lower power consumption also results from employing temperature responsive mechanical actuators in another aspect of the present invention.
According to an aspect of the present invention, an optical integrated circuit is provided that contains a base containing a first region and a second region separated by a hinge, and an AWG chip over the base, where a groove traverses one or more of one of the lenses and the waveguide grating, and an actuator connecting the first region and the second region of the base. The base and actuator have different thermal expansion coefficients. The actuator expands and/or contracts with temperature changes causing the first region and at least a portion of the AWG chip thereover to move with respect to the portion of the AWG chip over the second region. Thus, wavelength shift associated with waveguide temperature dependent refractive index can be mitigated.
According to another aspect of the present invention, optical integrated circuit is provided that contains an AWG chip with a groove traversing one or more of the lenses and the waveguide grating. The AWG chip contains a first region and a second region connected by a hinge and separated by the groove. An actuator connects the first region and the second region of the AWG chip. The AWG chip substrate and actuator have different thermal expansion coefficients. The actuator expands and/or contracts with temperature changes causing the first region of the AWG chip to move with respect to the second region. Thus, wavelength shift associated with waveguide temperature dependent refractive index can be mitigated.
Another aspect of the invention provides a methodology for fabricating an OIC capable of mitigating wavelength shift associated with waveguide temperature dependent refractive index. Fabrication of the OIC includes forming a groove in the AWG chip so that an actuator can induce relative movement between different portions of the chip in response to temperature changes.